In recent years, an electronic device including a portable phone and a car navigator tends to require much higher and a variety of functions. With this trend, a device having an optically transparent touch panel placed on front side of a liquid crystal element or other display element is increasing in number, in which the variety of functions is switched with the touch panel pressed by a finger or a pen, while a display of the display element is visually recognized in a rear side of the panel. In this circumstance, a touch panel having a superior transparent visibility and a secure operability is demanded.
A conventional touch panel of this type and its manufacturing method is explained hereinafter using FIGS. 3 and 4.
For easy understanding, thickness of constituent component is shown enlarged in the drawings.
FIG. 3 is a cross sectional view of a conventional touch panel; and FIG. 4 is an exploded perspective view of the same.
In the drawings, upper conductive layer 3 an optically transparent material made of indium tin oxide, tin oxide or the like is formed on an undersurface of upper conductive layer 1 an optically transparent and film-like material. Similarly, under conductive layer 4 an optically transparent material is formed on an upper surface of under-substrate 2 an optically transparent film-like material.
On an upper surface of under conductive layer 4, a plurality of dot spacers made of insulating resin is formed at predetermined intervals (not illustrated). In this structure, a pair of upper electrodes 3A made of silver or the like is formed with upper electrode 3, and a pair of under electrodes 4A is formed with under conductive layer 4 crossing upper electrodes 3A at right angles.
Spacer 5 is formed in a frame shape on a peripheral part of the undersurface of upper substrate 1 or on the upper surface of under substrate 2, attaching the peripheral parts of upper substrate 1 and under substrate 2 with an adhesive layer (not illustrated) applied to an upper and a lower surface of spacer 5, facing upper conductive layer 3 and under conductive layer 4 each other at a predetermined space.
Further, a plurality of wiring patterns 6A and 6B made of copper, silver or the like is formed on an upper and lower surface of film-like wiring pattern 6, and then an insulating layer (not illustrated) is formed on the upper and the lower surfaces of wiring pattern 6 except for its end portions, covering wiring patterns 6A and 6B.
A left end portion of wiring pattern 6 (left end in FIG. 3, hereinafter called “left end”) is held between a right end portion (right end in FIG. 3, hereinafter “right end”) of upper substrate 1 and under substrate 2, and a terminal portion of upper electrode 3A formed on the undersurface of upper substrate 1 and a terminal portion of under electrode 4A formed on the upper surface of under electrode 2 are attached to the left ends of wiring pattern 6A and 6B, with anisotropic conductive adhesive 7, a synthetic resin dispersed with conductive particles.
Still further, adhesive layer 8 is formed on an entire undersurface of under substrate 2, covered by removable sheet 9, thus constituting the touch panel.
Thus constituted touch panel, after removable sheet 9 being removed, is attached to a front side of liquid crystal or other display element with adhesive layer 8 formed on the undersurface of under substrate 2, and then which is installed on an electronic device. When installing, wiring pattern 6 is bent downward and the right end of wiring patterns 6A and 6B is connected to an electronic circuit (not shown) of the device by a connector or by soldering.
With this structure, when a finger or pen pressure is applied to an upper surface of upper substrate 1, upper substrate 1 is bent at the depressed point, contacting upper electrode 3 with under electrode 4 at the depressed point, while a display of the liquid crystal element is seen and recognized in a rear side of the touch panel.
Voltage is sequentially applied from the electronic circuit, through the plurality of wiring pattern 6A and 6B, to upper electrode 3A and under electrode 4A, then to upper conductive layer 3A and under electrode 4A crossing the upper electrodes at right angles. The electronic circuit detects the depressed point with an applied voltage ratio, switching the various functions of the device.
When manufacturing this type of touch panel, first adhering an identical size of upper substrate 1 and under substrate 2 with spacer 5, holding the left end of wiring substrate 6 between upper electrodes 3A and 4A which are extensively formed at the right end of upper substrate 1 and under substrate 2, by positioning so as the plurality of wiring patterns 6A and 6B be put on the plurality of upper electrodes 3A and under electrodes 4A.
Next, heating and pressing the upper surface of upper substrate 1 and the lower surface of under substrate 2 by a jig and tool while the substrates holding the left end of wiring substrate 6 between the two, for adhesively connecting the terminal portion of upper electrode 3A and under electrode 4A to the left end of wiring patterns 6A and 6B with anisotropic conductive adhesive 7, therewith connecting wiring substrate 6 to upper substrate 1 and under substrate 2.
Then, adhering adhesive layer 8 of which the underside being covered by removable sheet 9 to the undersurface of under substrate 2 by successively applying rollers from an end portion of such adhered substrate in such a way that a bubble is not taken in when rolling, completing a touch panel connected by wiring substrate 6.
Manufacturing of the touch panel is possible by a conversely arranged process too. In this case, first adhering adhesive layer 8 and removable sheet 9 to the undersurface of under substrate 2 on which under conductive layer 4 being formed, then applying rollers to such stack, adhering the stack to upper substrate 1 through spacer 5, and then finally heating and pressing the upper surface of upper substrate 1 and the undersurface of removable sheet 9, connecting wiring substrate 6 to upper substrate 1 and under substrate 2.
However, when manufacturing the panel in this order, adhesive layer 8 is also heated and pressed when the connecting portion between the substrates and wiring substrate 6 is heated and pressed, with a possibility that adhesive layer 8 is deformed at the connecting portion or adhesive power of adhesive layer is deteriorated.
Because of the reason, in a conventional manufacturing method, connecting wiring substrate 6 first by heating and pressing the connecting portion, and then adhering adhesive layer 8 and removable sheet 9 to the undersurface of under substrate 2. With this process, however, bubbles can be taken in between the undersurface of under substrate 2 and adhesive layer 8, sacrificing transparent visibility of the panel when it is attached to a liquid crystal or other display element peeling off removable sheet 9.
In order to prevent the bubble to be taken in, applying rollers successively from the end for considerably a long period of time to attach adhesive layer 8 to under substrate 2, so it is a time-consuming process.
As a prior art document relating the technology, Unexamined Japanese Patent Publication No. 2003-58319 is publicly known, for an example.
With above conventional touch panel, in order to obtain a touch panel without bubbles but a panel having a good transparent visibility, it becomes necessary to apply rollers successively from one end for a long period of time and prevent bubbles to be rolled in, thereby the manufacturing process becomes a time-consuming and of a high cost, leaving problems.